How can I avoid jackknifing a tractor trailer?
You can check the answer of the people under the question at Quora “jackknife tractor trailer“
About Delilah
Written by: Delilah
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How can I avoid jackknifing a tractor trailer?
You can check the answer of the people under the question at Quora “jackknife tractor trailer“
About Delilah
There are lots of misconceptions about jackknifing, so first of all I need to explain exactly what jackknifing is.
The first thing you need to understand is that jackknifing is a result of the tractor skidding, and not the trailer. If a trailer skids it’s not so serious since it comes back into line when you release the brakes and continue to drive forwards. If you don’t release the brakes however, the trailer could slide into a ditch or against parked cars or into oncoming traffic. This is known as trailer slew or trailer swing not jackknifing. If however, the tractor skids and you’re unable to correct it, the trailer pushing from behind will exaggerate the skid. The tractor will spin around and collide with its own trailer. This is jackknifing .
In order to avoid jackknifing therefore, you must do all you can to prevent the tractor from skidding in the first place, and in the second place, if you do skid, correct it before you jackknife. Jackknifing occurs when a vehicle is empty or when a load is badly distributed so that there is very little weight over the drive axle causing it to lose traction.
Try to load your trailer so that you have the maximum legal weight over the drive axle in order to give it lots of traction.
Learn to spread your braking over the longest possible distance especially when the road is slippery. This means keeping a safe distance behind other vehicles and anticipating when you may need to stop.
Avoid braking or decelerating on curves. Use your brakes when travelling in a straight line. Slow down a little more than necessary then release the brakes and drive around the curve.
Be especially careful on downhill turns. If you’re travelling downhill and turning left or right at an intersection don’t decelerate around the corner because the trailer will try to continue down the hill and take you with it, backwards. You may need to come to a halt or almost, then release the brakes and pull the trailer around the corner.
If you ever need to take avoiding action, avoid braking and swerving at the same time. Brake first. Slow down as much as you can, then release them to swerve. Once you’ve swerved you can re-apply the brakes if necessary. Modern trucks have anti-lock brakes which makes it easier to take avoiding action without the risk of jackknifing. Bear in mind that even though a loaded truck is not likely to jackknife, swerving could cause it to shed its load or overturn.
If, after taking all necessary precautions, your tractor does begin to skid, you should try to correct it in the usual way before it gets too far. Most truck drivers are skilled enough to do this.
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Make sure your tractor and trailer has trailer predominance this helps so much in preventing jackknifing, it basically in an event of emergency braking applies the brakes of the trailer with more pressure than the tractor, this is because if you apply more pressure to the tractor unit it can dip and cause air resistance to act on the front of the trailer causing it to move side to side.
Also make sure you have traction control otherwise your trailer has a higher chance of jackknifing as well as capsizing.
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That is a great question and you would be shocked at how may pro’s don’t know what to do. I’m even betting money that you get a lot of copied wiki answers. LOL
Jackknifing has a few main causes. It can be caused by slippery road condition, especially on a grade. by losing control when backing quickly (often also fatal) or most commonly by poorly maintained brakes.
The leading way to prevent this is to regularly check your brake camber. This is what that huge sign that says “All trucks stop here and check your brakes before proceeding.” is for. However oddly enough I usually only see other old timers doing this. I don’t know if is no longer required or if the ones who don’t bother never get to be old timers.
Your tractor is equipped with a “trailer brakes only” lever. It is there to help you get out of a jackknife situation (or out of trailer skew) and does a reasonable job of that however it is also the leading cause of the same problem.
A jackknife is caused when your tractor, not your trailer, goes into a slide or skid. It is less likely with a load (more weight on the drivers) but if it happens loaded it is way harder to stop. You see a lot of it driving off highway in the mud. The skid will slow the tractor but the weight of the trailer will cause it to continue in a straight line at the same speed and it will continue to push your tractor further into the skid. Because the trailer is pushing the back of your tractor you can’t just steer out of it and locking up all the brakes will not prevent the steering axel from continuing to drag and push you under. If not stopped it can cut the cab right off the tractor as it is scissored by the trailer. The correct response is to apply just the trailer brakes and no tractor brakes. As the trailer slows down it pulls the tractor out of the skid. You also should release those brakes as soon as you get straight again at the latest. Holding them can cause the tractor to swing around and go the other way in slippery conditions or worse start the trailer sliding too. I usually like to quickly apply and release the trailer brake. It keeps the trailer from skidding and gives a jerking action to the pull on the back of the tractor which can help dig your steering axel in. So far as the steering goes you ignore the trailer and steer into the skid the tractor is having, as you would with a car, the only difference is that you keep the power constant, slowly increasing it as your straighten out. Slowing as you would in a car only makes things worse as the trailer isn’t slowing with you.
Common backing scenario is y ou spin out on a long grade and find the ground is too slippy to prevent you from sliding backwards and your gaining speed. If you keep that up you can quickly find that your backing up too fast to make the correction and the first time you make the wrong one you lose. The trailer goes sideways and you go under it. Backing runaways are the very worst, you can’t see, you can’t stop and you can’t control it. So when you first spin out do not stop, apply a little fuel and try to dig yourself a rut to stop in. If you can’t, you should immediately and deliberately back your trailer into the ditch. That is where it is going to end up anyhow so better to do it while your still going slow enough not to hurt anything. Especially yourself. I even got to watch a guy do that on black ice. He was still moving slow enough when he backed into the ditch the softer ground slowed the trailer, the dollies hung up, the tractor continued to slide, he cranked the wheel to follow the trailer in, then hit the fuel and low and behold if he didn’t just come out of the ditch, now going down the hill the other way. On the radio he told me he’d bent the dollies, scrambled up the load, and ruined his pants but other wise everything seemed fine.
Trailer skew is close to the same thing only it is the trailer that skids not the tractor. This is way more common for highway drivers. An icy downgrade for example, especially one with a skew in surface, can see your trailer decide to pass you. Even a windy day can do this to an empty cargo trailer on dry ground. The correct response is the same, you apply only trailer brake. However with trailer skew you also apply fuel (very hard to do, it goes against your instincts when in trouble). The idea is to out run the trailer and pull it back in behind you. Grocery truck is always empty going home and ice and wind are the common days here. I have spent entire afternoons on icy highways in the wind doing this about every twenty minutes at random all the bloody way home. I don’t like it.
Unfortunately one of the leading causes of jackknifing is dealing with trailer skew, mud and jackknifing (or an owner operator). When you only apply the trailer brakes you only wear out the trailer brake pads. After doing that for even a short while you find that the pads on your tractor are fully applied when your worn trailer pads are not. Your tractor slides and your trailer does not… presto jackknife. I’m going to squeal on my buddies here too. Owner operators in a freight yard own the tractor only, the company owns the trailers. It doesn’t take them long to figure out, especially with a train, that there are more than enough brakes on the trailers to stop you on good roads so why burn up your own pads, they are expensive, just use the trailers. Ya guys so you know, your not fooling anyone. I can smell that drivers trailer pads from 25 feet and I have to set them to match my tractor. We know what you did there so stop being a cheep turd, that is your tractor your endangering, not mine.
Last big cause of a jackknife is poorly set up brakes and I have even seen that taught incorrectly at a professional driving course. If you will actually stop and check your brakes like you should (I do so every morning, pre trip, every time I leave the bush, mud, or hilly county, at everyone of those big signs, and every time I take my chains off, and at the end of every day. It’s my arse on the line) it is important that you do it correctly. If you have been told to close your slack adjuster and then back it off 1/2 of a turn please stop that immediately before you kill yourself. It is a common and huge error. Your trailer was made by one company, they used a particular type or make of slack adjuster. Your tractor was made by a different company, different adjuster. Now lets say the ones on your trailer have course threads and the ones on your tractor have fine threads. You just took the time and effort to set your rig up for a jackknife. Your tractor brakes only backed off by 1/4 of an inch while your trailer got 1/2 of an inch and your in trouble.
To do this by yourself. I like 1/4″ of an inch of slack, will leave them till I have 1/2″ or am bored and then take them all back down. If you have more than 3/4″ your brakes are out of adjustment. When the drum gets hot it expands and you can find that your brakes no longer contact the drum. My brake kit is a closed wrench that I cut a little mark into on the open end at 1/4″ and on that wrench the jaws were 1/2″ wide, and a long heavy screwdriver (I picked one with a big heavy handle, it makes a great tire thumper too). With your truck chocked and your brakes off insert the screwdriver into the slack adjuster yoke and physically close the brake. Use the marked end of the wrench to measure how far it moved either against the push rod or using the yoke pin. If you have to adjust one you should do them all. The idea is to get them as close as possible to each other so they all apply in unison. If I had more than 1/2″ on any I did them all.
Many modern trucks have automatic slack adjusters but you still should check them. Most newer trucks also have anti-lock brakes. If your driving one that does not have these features and you drive in bad conditions it is not a bad idea to leave your steering axel with just a slightly larger gap. The thinking behind this is that if you have to make an emergency stop and lock it up you will still be able to steer as your front brakes will apply last and release first. With anti-lock brakes this is not a good idea at all. Braking power is the one thing that you can never get enough of in a rig. Ever. I’ve even been known to wish mine had a parachute.
Keep the shiny side up.
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